1. Field of the Invention
The present invention relates in general to an apparatus and a method of producing a battery case, and more particularly to improvements in an apparatus and a method of producing a battery case having a tubular shape with a closed end, by performing plural sorts of press working including DI (drawing and ironing) processing.
2. Discussion of Related Art
As well known, most of dry batteries and secondary batteries are constituted such that various sorts of electricity-generating elements suitable for the respective batteries are accommodated inside a metal battery case (battery can) having a tubular shape such as cylindrical or prismatic with one of its opposing ends closed. In each of such batteries, the battery case, as a shell body of the battery, needs to be light in weight and have a structure which withstands increased internal pressures during its use.
In view of the above, there is a recently proposed technique of producing a battery case by utilizing DI (drawing and ironing) processing capable of forming a metal tubular body having a small wall thickness and a sufficiently high degree of pressure withstanding strength, namely, by utilizing a press working method in which drawing and ironing are successively performed, as disclosed in WO00/69004, for instance.
Described more specifically, in the proposed technique, a drawing operation is initially performed on a plate-like metal material using a blanking die and a blanking punch, whereby a metal blank with a predetermined shape is obtained. The thus obtained metal blank is then subjected to a drawing operation using a drawing die and a drawing punch, thereby forming a tubular intermediate product having a closed end and a small depth. Subsequently, the intermediate product is subjected to DI processing wherein a plurality of redrawing operations and a plurality of ironing operations are successively performed using (i) a DI punch, (ii) a first die assembly (die mechanism) including a plurality of redrawing dies whose die holes have mutually different sizes and which are arranged in the order of the sizes of the die holes, and (iii) a second die assembly (die mechanism) including a plurality of ironing dies whose die holes have mutually different sizes and which are arranged in the order of the sizes of the die holes. Consequently, there is formed an intended battery case, which has a tubular shape having a closed end and a larger depth and a smaller wall thickness than the intermediate product. According to the proposed technique, it is possible to obtain, with high reliability, a battery case that is light in weight and has a structure that withstands increased internal pressure of the battery during its use.
In the proposed technique of producing the battery case, however, the step in which the plate-like metal material is formed into the intermediate product is carried out using a press machine exclusively for successively performing the blanking and the drawing, and thereafter the step in which the intermediate product is formed into the intended battery case is carried out using another press machine exclusively for performing the DI processing. Therefore, the proposed technique suffers from the following disadvantages.
Namely, where the battery case is produced according to the aforementioned conventional technique, space is needed for installing the two press machines. Further, in addition to the two press machines, a transfer device must be installed for transferring the intermediate product formed by one of the two press machines to the other. Thus, an enormous equipment investment is required, undesirably pushing up the cost of manufacture of the battery case.